Copying system featuring combined developing-cleaning station alternately activated

ABSTRACT

Electrophotographic copying apparatus has charging, imaging, transferring, precleaning, and erasing facilities in a conventional sense but incorporates a combined developingcleaning unit that is operable to perform either function at the proper time during the copying sequence. A first version incorporates a photoconductor drum structure surrounded with the necessary electrophotographic elements including a single developer-cleaner unit. Another version incorporates a photoconductor belt movable forwardly and reversely. In either version, cleaning cycles may alternate with developing cycles or be activated following the production of a high number of images on the photoconductor surface. Conveniently, a magnetic brush element forms a contacting surface for conveying toner onto the photoconductor surface during developing and for scavenging residual toner from the photoconductor surface by bringing developer mixture into contact with the photoconductor surface during cleaning. Appropriate changes in biasing of the brush are made during operation.



1. Electrophotographic apparatus for producing at least one copy from an original document and having the customary electrophotographic facilities for charging, imaging, transferring, precleaning, and erasing a photoconductor medium, said photoconductor medium comprising a movable member having an endless surface, comprising: a combined developer-cleaner unit positioned for engagement with said photoconductor medium at a single station for developing an image on said photoconductor medium in one mode and cleaning said photoconductor medium in another mode; and means for selectively activating said developer-cleaner unit in one or the other of said modes during operation of the said apparatus.
 2. The apparatus of claim 1 wherein said photoconductor medium comprises a rotatable cylindrical drum member accommodating an image area thereon during operation of said apparatus, and further comprising: sequencing means for activating said developer-cleaner unit to develop and clean said drum member in an alternative fashion during rotation of said drum member.
 3. The apparatus of claim 2, further comprising: means for rotating said drum member during successive cycles of operation of said apparatus to produce a multitude of copies; means to activate said developer-cleaner unit in a developer mode continuously during said successive cycles of operation of said apparatus and rotation of said drum member; and runout means operable upon termination of said successive cycles and production of a multitude of copies to activate said developer-cleaner unit to clean said photoconductor drum member in readiness for a succeeding multiple copy run.
 4. The apparatus of claim 1, wherein: said photoconductor medium is in the form of an endless belt member mounted for movement in a preferred direction to convey an image area past the various stations in said apparatus during operation; and means operable in successive cycles and movement of said belt member for activating said developer-cleaner unit to devElop an image in one cycle and clean an image in the next cycle on said belt member.
 5. The apparatus of claim 1 wherein said photoconductor medium is an endless belt member mounted for movement in a preferred direction during operation of said apparatus to convey an image area past the various stations in the course of producing copies, and further comprising: means for activating said developer-cleaner unit to develop each succeeding image on said photoconductor belt member during operation and the production of a multitude of copies; and means for activating said developer-cleaner unit to clean said photoconductor belt member upon termination of a run of said multitude of copies.
 6. The apparatus of claim 1 wherein said developer-cleaner unit comprises a housing to accommodate a developer mixture including toner, and further comprising: a magnetic brush mounted within said housing and in contact with said photoconductor medium at a single station for conveying developer mixture onto said photoconductor medium in one mode for the purpose of developing images on said photoconductor medium and for cascading developer mixture onto said photoconductor medium in a scavenging mode for the purpose of cleaning said photoconductor medium; and sequencing means for activating said developer-cleaner unit and said magnetic brush member in the appropriate mode required during operation of said apparatus.
 7. The apparatus of claim 6, further comprising: means for producing positive and negative biasing potentials; means connecting said magnetic brush member to said potential producing means during operation of said apparatus; and means for selectively applying one or the other of said potentials as a bias to said magnetic brush member to create the repulsion necessary to transmit toner from said magnetic brush member to said photoconductor medium during a developing mode and to create the attraction relationship to scavenge toner from said photoconductor medium to said magnetic brush member during a cleaning mode.
 8. The apparatus of claim 1, further comprising: means for activating said developer-cleaner unit to develop at least one image on said photoconductor member from an original document during operation; and means for activating said developer-cleaner unit when a different original document is positioned in said apparatus to clean said photoconductor belt member. 